Re: [boost] [smart_ptr] trunk versionof enable_shared_from_thisincompatible with TR1

From: Peter Dimov (pdimov_at_[hidden])
Date: 2008-04-30 13:42:15

Frank Mori Hess:
> On Tuesday 29 April 2008 13:03 pm, Peter Dimov wrote:
>
>> We need to flesh out the specifications of the changes we are
>> proposing.
>
> One effect sp_accept_owner (and shared_from_this in constructors) have on 
> the > existing specifications is they put a big asterisk on the 
> postconditions of
> some of the shared_ptr constructors.  Really, all bets are off 
> postcondition
> wise after sp_accept_owner has been called, unless restrictions are placed 
> on
> what sp_accept_owner is allowed to do.  Specifying that sp_accept_owner
> cannot modify its shared_ptr argument, as you suggested earlier, would 
> allow
> some postconditions to be preserved, although not the ones
> involving "use_count() == 1".

This is a very good point, probably even a showstopper for an eventual 
sp_accept_owner proposal.

I note that creating a long-lived shared_ptr in the constructor breaks the 
postcondition as well. Annoying.

In principle, a new esft may avoid this by:

1. Allowing only (expired) weak_ptr instances to be created in the 
constructor;
2. Bringing the weak_ptr instances back to life once a shared_ptr takes 
ownership.

This however seems to require a relatively major surgery to sp_counted_base 
and friends; I'm not sure I'm comfortable with that.